As a method for imparting water/oil repellency to the surface of an article (such as a fiber product), a method of treating the article by means of a water/oil repellent composition composed of a solution having dissolved in or an emulsion having dispersed in a medium, a fluorinated compound having various polyfluoroalkyl groups (a polyfluoroalkyl group will be hereinafter referred to as a Rf group), particularly a fluorourethane compound or a fluoropolymer, has been known.
In Patents Documents 1 and 2, as a fluorourethane compound having an Rf group, a fluorourethane compound which is a reaction product of a polyisocyanate and a fluoroalcohol having an Rf group having at least 8 carbon atoms (including other alcohols) has been used.
However, recently, EPA (US Environmental Protection Agency) has pointed out that a compound having a perfluoroalkyl group (a perfluoroalkyl group will be hereinafter referred to as a RF group) having at least 8 carbon atoms is likely to be decomposed in the environment or in vivo, and the decomposition product is likely to be accumulated, i.e. it presents a high environmental impact. Therefore, a water/oil repellent composition has been required which has an RF group having at most 6 carbon atoms.
Patent Document 3 discloses a fluorourethane compound which is a reaction product of a fluoroalcohol having an RF group having 4 carbon atoms and a sulfonyl group, and a polyisocyanate, for reducing the environmental impact. However, the water/oil repellency of articles treated with a water/oil repellent composition comprising the above reaction product is insufficient.
Patent Document 4 discloses a urethane compound which is formed by a reaction of a fluoroacryl oligomer having an RF group having at most 4 carbon atoms and a hydroxyl group at its terminal, and a polyisocyanate. For the production of the urethane compound, two steps are required: a step of polymerization for forming an oligomer having a functional group which is reactive to an isocyanate at a terminal and a step of reacting the oligomer and an isocyanate. Thus, such a production process is complicated.